A prior art dual capstan drive unit for a tape recorder has controlled the revolution speed of two capstans by comparing variable frequency signals generated in response to revolutions of the capstans with reference frequency signals from respective oscillators. The drive unit may be applied to a dual capstan type reversible tape recorder. In case the two capstans have the same outer diameter and the generated frequencies are equal to each other when two capstans rotate at the same speed, two different reference frequency signals may be established corresponding to upstream and downstream capstans for obtaining a given tape tension and switched in accordance with the direction of transport of a magnetic tape so that each peripheral speed of the upstream and downstream captans can be set at the same speed in both directions of the tape transport. However, in case the capstans have the outer diameter different from each other, two different reference frequency signals are required in each of the directions of the tape transport. Thus, it will be noted that additional oscillators and frequency dividers are required, and as a result the drive unit is disadvantageously uneconomical.